Electrostatic spinning of solutions of fiber-forming polymers is well known. Electrostatic spinning of polyurethane solutions to form fine diameter fibers is also known as described for example in U.S. Pat. Nos. 4,043,331 and 4,044,404.
The process of electrostatic spinning of polyurethanes and other fiber-forming polymers involves the introduction of a solution of the polymer into an electrostatic field where droplets of the solution are attenuated into fibers while being drawn to an electrode where the fibers are collected. The spinning environment is controlled to evaporate the solvent while the fibers are being formed in the electrostatic field so that the fibers collected on the electrode retain their individual identity. Some fusing between fibers at points of intersection may occur, and is often desirable, as a result of residual solvent content in the fibers. Eventually, residual solvent is removed from the mat of collected fibers as part of the total spinning process.
The fibers obtained by the electrostatic spinning process are thin, generally in the order of 0.1 to 25 microns, and preferably 0.5 to 10 microns. Fibers having different characteristics are obtained by adjusting the spinning conditions including the molecular weight and concentration of polymer in the spinning solution. In all cases however, it is essential that the spinning solution be a composition which is capable of being attenuated in the electrostatic field. Some problems have been experienced in producing fibers of uniform diameter from certain polymer solutions, including solutions of polyurethanes.
It is accordingly an object of the present invention to provide a polyurethane polymer which is particularly suitable for use in the electrostatic spinning of fine fibers. It is a further object of this invention to provide a process for the preparation of the aforesaid polyurethane polymers. These and other objects of the present invention will be apparent from the ensuing description and claims.